Displacement devices are known, e.g. from DE AS 1780488, EP 0503954 A1, and DE 19944684 C1.
Further, WO 02/070328 A1 discloses a displacement device having two guide rails with toothed beams, wherewith a slide or carriage is slidably disposed on said rails, which slide bears a fifth wheel coupling. The displacement device is disposed on the slide, and has locking pieces which engage the toothed beams.
In addition to horizontal displacement of the fifth wheel coupling, it is also possible to raise and lower the fifth wheel coupling, wherewith the semi-trailer will have different heights or altitudes, for desired adjustment purposes. Lifting devices are known which can accomplish such raising and lowering, e.g. as disclosed in DE 198929 A1 or DE 19839357 A1.
The fifth wheel coupling must bear appreciable forces not only in the vertical direction but also in the direction of travel and in the lateral direction; accordingly, the fifth wheel coupling must be robust and stable with respect to the vehicle frame(s) in all directions, whether in a raised or in a lowered position. In this connection, the lifting device according to DE 19828357 A1 has a base plate to which lever arms are swingably mounted so as to be swingable around a horizontal axis. The fifth wheel coupling and adjusting arms are disposed at the other end of the lever arms. Pressure cylinders are disposed between the adjusting arms and the lever arms, which cylinders serve to raise and lower the lifting device. This lifting device can be remotely operated, but the driver must locally check or observe and verify the particular lifting altitude.
The heretofore known displacement and lifting devices are designed to adjust to the given configuration of the tractor and semi-trailer prior to the driving of the vehicle. However, it has been found that the intermediate space or gap between the front of the semi-trailer and the cab of the tractor experiences or causes aerodynamic turbulence while the vehicle is being driven, which turbulence influences the air resistance and thereby the fuel consumption of the tractor and semi-trailer combination.
In order to counteract this turbulence effect, wind deflectors are often employed to cause the air to stream over the gap in a controlled manner. Such deflectors are heavy and costly, and are installed in a fixed position. Any change in the deflector configuration must be performed manually, which generally requires intervention by the adjusting individual in the gap itself.
In principle, it is desirable to arrange for the described intermediate space or gap to be as small as possible. However, if the gap is too small, the corners of the semi-trailer will strike the rear wall of the cab of the tractor when the vehicle is negotiating a curved path.
Situations may also arise when it is desirable to have a large gap, e.g. in order to provide space for special equipment, or while parked to increase the accessibility to the supply lines running to the semi-trailer.
Known displacement devices allow the semi-trailer to be displaced, but they require the driver to unlock the displacement device mechanism and then change the gap by moving the tractor, then to re-engage the mechanism and judge whether the mechanism is now properly re-engaged and locked. This process involves appreciable physical stress and exertion by the driver, which may indeed injure the driver. Further, the adjustment requires the vehicle to be stationary; it cannot be performed while the vehicle is underway.